optique

name	optique
description	Use this skill when writing any code that builds a command-line interface with Optique in TypeScript or JavaScript. Covers the combinatorial parser model, choosing @optique/core vs @optique/run, value parsers, structured messages, optional()/withDefault()/multiple(), subcommands with command() and or(), shell completion, async parsing, the integration packages, and common mistakes to avoid. Trigger whenever the user is parsing command-line arguments, building a CLI, or adding options or subcommands to a tool.
license	MIT

Start at https://optique.dev/llms.txt when online. These rules cover the combinatorial parser model and common pitfalls offline.

Core rules

• Use run() from @optique/run for applications; use parse() or runParser() for embedded and custom runtimes.
• With runParser(), onError(exitCode, error) supplies a structured Message; help.onShow(exitCode, page) supplies the final DocPage. Both follow output. Supply stdout: () => {} for custom help rendering. See https://optique.dev/concepts/runners.md#structured-help-callbacks.
• In tests, use parseArgs()/parseArgsSync() from @optique/testing/parser for parser results, captureRun() from @optique/testing/run for runner output/exits, captureProgramRun() from @optique/testing/discover for dispatch, and createCliRunner() from @optique/testing/cli for real CLIs.
• Compose parsers with object(), tuple(), seq(), or(), merge(), and modifiers. Do not hand-write argument scanners around Optique parsers.
• Let TypeScript infer the parsed value type from the parser. Do not hand-maintain a separate interface for the result unless another API boundary requires it.
• Most parsers are required until you wrap them. optional(p) yields undefined; withDefault(p, value) yields a fallback value. For Boolean flags, use withDefault(flag("--name"), false) when absence should mean false.
• Use semantic message helpers for descriptions and errors. Since 1.3.0, customize terminal output with theme or messageFormatter, preserving initialWidth, quoting, and width options. Keep canonical errors unthemed.
• Use value parsers such as integer(), choice(), biject(), regExp(), url(), and uuid() instead of validating raw strings after parsing. Use regExp({ flags }) for user-supplied regular expression sources, biject() for one-to-one string-to-value choices, and transform() when an existing value parser describes the accepted CLI spelling but your app needs a different result type. Use path() from @optique/run/valueparser for file-system paths. Write a custom { mode, metavar, parse, format } value parser only when the catalog does not cover the domain.
• Async value parsers make the containing parser async. If you use packages such as @optique/git, remember to await run(...), await parse(...), or await runParser(...) as appropriate.
• Use dependency() when one value parser controls another's valid values. For a multi-level chain, wrap the middle derivation too: dependency(source.deriveSync(...)). Optique resolves such chains by dependency order, independently of object/tuple field order.
• Use derivePromptConfig(source, resolver) (from @optique/prompt, re-exported by @optique/inquirer and @optique/clack) when a prompt's choices or message depend on another parsed value. The resolver may be async and runs only at the real prompt fallback, after the named sources resolve; pass [sourceA, sourceB] when it reads several sources. The resolver's prompt kind must return the wrapped parser's value type. Derive the wrapped parser separately when the CLI domain should change, and make it a dependency source only if another consumer needs its answer. Keep static prompt configs for everything else.
• Pass { validate, maxAttempts, signal } as a generated prompt wrapper's third argument, including prompt() from @optique/inquirer and @optique/clack. The validator returns undefined to accept the prompted value or a structured Message to retry, synchronously or asynchronously. Attempt limits must be positive integers and default to unlimited retries. Selection prompts keep their config and use the shared validate option.
• Implement a custom adapter's execute(config, context) so retries can show context.previousValidationMessage, and forward context.signal when the prompt library supports aborting active work. Adapter-native validation remains separate and completes inside one shared attempt.
• Build subcommands with command() combined by or(). Put a literal field such as command: constant("serve") in each branch when you want a discriminated union.
• Enable completion through run(parser, { completion: "both" }) for CLI apps. Do not hand-write completion scripts from parser metadata.
• Use usageLine: [{ type: "ellipsis" }] in runner options when a large root synopsis should become a compact Usage: myapp ... line. This applies only to root full help; use command()'s usageLine for subcommand help.
• Use showUsage: false in runner options when full help should show the brief and command or option sections without the Usage: synopsis. For deeply nested command trees, add commandList: "top-level" when root help should list only first-level command groups.
• Use termWidth: "auto" in runner options when descriptions should align after the widest visible help term. Optique measures terminal display width after adding built-in help/version/completion entries.

Canonical app shape

import { object } from "@optique/core/constructs";
import { message } from "@optique/core/message";
import { withDefault } from "@optique/core/modifiers";
import { argument, flag, option } from "@optique/core/primitives";
import { integer, string } from "@optique/core/valueparser";
import { run } from "@optique/run";

const parser = object({
  input: argument(string({ metavar: "FILE" }), {
    description: message`Input file to process.`,
  }),
  port: withDefault(
    option("--port", integer({ min: 1, max: 65535 }), {
      description: message`Port to listen on.`,
    }),
    3000,
  ),
  verbose: withDefault(
    flag("-v", "--verbose", { description: message`Enable verbose logging.` }),
    false,
  ),
});

const config = run(parser, {
  brief: message`Process a file.`,
  completion: "both",
  showDefault: true,
  termWidth: "auto",
});

console.log(`Processing ${config.input} on port ${config.port}.`);

Subcommands

Use command() for each branch and or() to require exactly one matching subcommand. Use optional(or(...)) only when no subcommand is valid.

import { object, or } from "@optique/core/constructs";
import { withDefault } from "@optique/core/modifiers";
import { parse } from "@optique/core/parser";
import { command, constant, flag, option } from "@optique/core/primitives";
import { integer } from "@optique/core/valueparser";

const parser = or(
  command("build", object({
    command: constant("build"),
    watch: withDefault(flag("--watch"), false),
  })),
  command("serve", object({
    command: constant("serve"),
    port: withDefault(option("--port", integer({ min: 1 })), 3000),
  })),
);

const result = parse(parser, ["serve", "--port", "8080"]);

if (result.success) {
  switch (result.value.command) {
    case "build":
      result.value.watch;
      break;
    case "serve":
      result.value.port;
      break;
  }
}

Custom value parsers

Prefer the built-in catalog first. If a one-to-one dictionary can describe the input tokens and domain values, use biject(). If an existing parser already accepts the right input syntax, wrap it with transform() before writing a custom parser:

import { biject, choice, transform } from "@optique/core/valueparser";

const exitCode = biject({
  ok: 0,
  warning: 1,
  error: 2,
});

const logLevel = transform(choice(["debug", "info", "warn", "error"] as const), {
  map(value) {
    return value.toUpperCase() as "DEBUG" | "INFO" | "WARN" | "ERROR";
  },
  unmap(value) {
    return value.toLowerCase() as "debug" | "info" | "warn" | "error";
  },
});

When a custom domain is needed, keep the validation in a value parser so help, errors, defaults, prompts, and completion all see the same typed value.

import { message } from "@optique/core/message";
import type { ValueParser, ValueParserResult } from "@optique/core/valueparser";

const levels = ["debug", "info", "warn", "error"] as const;
type Level = typeof levels[number];

function isLevel(input: string): input is Level {
  return (levels as readonly string[]).includes(input);
}

function logLevel(): ValueParser<"sync", Level> {
  return {
    mode: "sync",
    metavar: "LEVEL",
    placeholder: "info",
    parse(input: string): ValueParserResult<Level> {
      if (isLevel(input)) return { success: true, value: input };
      return { success: false, error: message`Invalid log level: ${input}.` };
    },
    format(value: Level): string {
      return value;
    },
  };
}

const parser = logLevel();

Common mistakes checklist

• Do not parse process.argv manually before calling Optique. Pass the parser to run() for applications, or pass explicit argument arrays to parse() in tests and embedded use.
• Do not treat or(a, b) as “zero or more alternatives.” It requires one matching branch unless the whole or() is wrapped in optional() or withDefault().
• Do not use object() for mutually exclusive subcommands. Use or(command(...), command(...)).
• Do not forget that flag("--x") is required. Wrap it in optional() or withDefault(..., false) for ordinary optional flags.
• Do not expect multiple(p) to fail when absent; it returns []. Wrap with nonEmpty() when at least one value is required.
• Do not confuse free-order parsing with seq(). Most constructs let child parsers compete by priority; use seq() only for truly ordered grammars.
• Do not concatenate plain strings for errors or descriptions. Use structured message values.
• Do not forget to register source contexts when using bindEnv(), bindConfig(), or bindDerivedDefault().
• Do not flatten a multi-level dependency graph into duplicated one-level factories. Wrap each derived value that becomes a later source with dependency() and derive the next parser from it.
• Do not probe runtime capabilities eagerly before constructing a prompt parser. Put synchronous or asynchronous checks in the prompt config's when field and provide a typed otherwise value. The check then runs only if parsing reaches the prompt fallback.

For the detailed maintained guide, use https://optique.dev/pitfalls.md.

Reference links

• Documentation index for agents: https://optique.dev/llms.txt
• Runners and entry points: https://optique.dev/concepts/runners.md
• Primitive parsers: https://optique.dev/concepts/primitives.md
• Construct combinators: https://optique.dev/concepts/constructs.md
• Modifiers: https://optique.dev/concepts/modifiers.md
• Value parser catalog: https://optique.dev/concepts/valueparsers.md
• Inter-option dependencies: https://optique.dev/concepts/dependencies.md
• Structured messages: https://optique.dev/concepts/messages.md
• Shell completion: https://optique.dev/concepts/completion.md
• Command discovery: https://optique.dev/concepts/discover.md
• Man pages: https://optique.dev/concepts/man.md

Integration packages

Package	Use for	Docs
@optique/env	Environment variable fallbacks	https://optique.dev/integrations/env.md
@optique/config	Configuration file fallbacks	https://optique.dev/integrations/config.md
@optique/derived-defaults	Defaults computed from first-pass results	https://optique.dev/concepts/derived-defaults.md
@optique/prompt	Generic prompt adapter foundation	https://optique.dev/integrations/prompt.md
@optique/clack	Clack interactive fallback prompts	https://optique.dev/integrations/clack.md